FIG. 1 shows the configuration of a furnace of a continuous annealing line which is provided in an integrated steelworks.
In the furnace 10 of the continuous annealing line, the temperature of a strip introduced into the intake side of the furnace 10 is increased as the strip is preheated in a preheating section 11 using gas discharged from a heating section 12 and is indirectly heated via radiant tubes in the heating section 12.
The strip that has passed through the heating section 12 is heat-treated at a uniform temperature in a uniformly-heating section 13, and is slowly cooled in a slow cooling section 14 through circulation cooling of an atmospheric gas.
In addition, the strip that has passed through the slow cooling section 14 is cooled in a rapid cooling section 15 using a main gasket, a cooling role and an auxiliary gasket, is subjected to overaging in an overaging section 16, and is cooled in a final cooling section 17.
In the above-mentioned furnace 10 of the continuous annealing line, grains inside the strip are recovered and recrystallized in the preheating section 11 and the heating section 12 and grow in the uniformly-heating section 13.
In addition, the solubility of dissolved carbon is increased in the slow cooling section 14 where the temperature of the strip is lowered, and the dissolved carbon is supersaturated in the rapid cooling section 15. A carbide (Fe3C) produced through the supersaturation of the dissolved carbon precipitates in the overaging section 16.
As methods of controlling the strip temperature in the rapid cooling section 15 of the furnace 10 of the continuous annealing line, several technologies have been proposed in the related art.
One of the several technologies of the related art was disclosed in Korean Laid-Open Patent Publication No. 2005-0051023, titled “METHOD OF CONTROLLING COOLING RATE OF STRIP IN RAPID COOLING SECTION OF CONTINUOUS ANNEALING LINE.”
This method of the related art relates to a method of controlling the cooling rate of a strip in a cooling section of a continuous annealing line. According to this method, cold rolled steel sheets having uniform quality can be produced since the cooling rate and the carbon concentration of the strip that passes through the rapid cooling section can be uniformly maintained.
In addition, “APPARATUS FOR COOLING STRIP IN ANNEALING FURNACE” disclosed in Korean Laid-Open Patent Publication No. 2004-0047308 relates to an apparatus for uniformly cooling a strip subjected to processing in a rapid cooling section of an annealing furnace such that the strip is cooled to a target temperature. This invention intended to provide uniform cooling using roll cooling in which cooling water is supplied to a roll.
Furthermore, “COOLING CONTROL METHOD FOR STRIP IN COOLING SECTION OF CONTINUOUS ANNEALING FURNACE” disclosed in Korean Laid-Open Patent Publication No. 2003-0054513 proposed a method of controlling the cooling of a strip by controlling variations in the power of a cooling fan in a cooling section of a continuous annealing furnace.
However, all of these technologies of the related art are intended to control the lengthwise temperature of the strip, and it is therefore impossible to control the widthwise temperature of the strip.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method and apparatus for uniformly controlling a strip temperature in a rapid cooling section of a continuous annealing line which can control the widthwise temperature distribution of a strip which moves in the vertical direction such that the widthwise temperature distribution has an intended profile, thereby eventually minimizing flatness defects which would otherwise occur due to non-uniform cooling of the strip.
Another object of the present invention is to provide a method and apparatus for uniformly controlling a strip temperature in a rapid cooling section of a continuous annealing line which can measure the temperature using widthwise thermometers in intake and discharge ends of the rapid cooling section of the continuous annealing line and uniformly control the widthwise temperature of the strip through flow rate control over mist sprayed in the rapid cooling section using a feedback/feedforward control technique, thereby minimizing changes in the flatness of the strip.